The present invention relates generally to a control system for a compressor. More specifically, the present invention relates to a capacity modulation system for a compressor that can automatically adjust the capacity of the compressor in a heat pump during a heating operation.
Frequently, motors for driving compressors in heating, ventilation and air conditioning (HVAC) systems are designed to operate from standard line (main) voltages and frequencies (e.g., 230 V, 60 Hz) that are available at the location where the HVAC system is being operated. The use of line voltages and frequencies results in the motor being limited to one operating speed that is based on the input frequency to the motor. The operation of the motor at one speed, in turn, results in the compressor being limited to a single output capacity. Furthermore, motors that require their own controller or electronic drive, e.g., switched reluctance motors, cannot be used for these HVAC systems, as such motors cannot operate directly from standard (main) voltages and frequencies.
One problem with the compressor being limited to a single output capacity is that the compressor, especially a reciprocating compressor, has a limited heating capacity at reduced outdoor ambient temperatures. This limited heating capacity produced by the compressor adversely affects the EER (Energy Efficiency Rating) and HSPF (Heating Season Performance Factor) of any system incorporating the compressor during testing and in subsequent operation of the system. Furthermore, the limited heating capacity output of the compressor at reduced outdoor ambient temperatures requires additional (and more costly) heating techniques to be used to maintain a setpoint temperature in an enclosed space.
Therefore, what is needed is a cost-effective, efficient and easily implemented system to boost the heating capacity of a compressor at reduced outdoor ambient temperatures.